1. Field of the Invention
The invention relates to a universal joint yoke, a universal joint, and a vehicle steering apparatus.
2. Description of the Related Art
A universal joint is, for example, used in a vehicle steering apparatus. The universal joint includes a pair of yokes that are swingably coupled to each other via a cross shaft or an X-shaped shaft. Japanese Utility Model Application Publication No. 4-122224 (JP-U-4-122224), Japanese Patent Application Publication No. 2007-333189 (JP-A-2007-333189) and Japanese Patent Application Publication No. 54-118937 (JP-A-54-118937) describe that a yoke has a cylindrical portion for fixing a shaft and a pair of arms that extend parallel to the axial direction of the cylindrical portion. The pair of arms extend from one end of the cylindrical portion. Japanese Patent Application Publication No. 3-9118 (JP-A-3-9118) also describes a yoke that has a cylindrical portion for fixing a shaft, a pair of arms that extend parallel to the axial direction of the cylindrical portion, and a flat plate provided at one end of the cylindrical portion. The flat plate is arranged perpendicularly to the axial direction of the cylindrical portion. The arms project from the flat plate in the axial direction of the cylindrical portion.
Japanese Patent Application Publication No. 2003-287052 (JP-A-2003-287052) describes a yoke that has a pair of arms and a flat plate that connects the pair of arms to each other. The flat plate is arranged perpendicularly to the axial direction of a shaft. The shaft is directly welded to the flat plate.
According to the structures described in JP-U-4-122224, JP-A-2007-333189, JP-A-54-118937 and JP-A-3-9118, to fix the shaft to the cylindrical portion of the yoke, it is necessary to, for example, weld the shaft to the cylindrical portion at expense of time and effort. This also applies to JP-A-2003-287052. On the other hand, to make it easy to fix the shaft, the cylindrical portion of a universal joint yoke may have a slit that extends in the axial direction of the cylindrical portion. For example, first and second tabs are provided respectively on both sides of the slit so as to face each other. A bolt is inserted through a bolt insertion hole of the first tab and screwed into a screw hole of the second tab, thus fastening the shaft with the cylindrical portion. However, the slit decreases the strength of the cylindrical portion and, as a result, the life of the yoke shortens. Conversely, when the yoke is formed to be thick so as to extend the life of the yoke, the size of the yoke increases.